Accuracy of displayed volume with three airway sensors in an animal model

Abstract

Optimal mechanical ventilation in infants and pediatrics depends on the reliability of flow sensors to correctly measure flow and integrate it into accurately displayed tidal volumes (V_TE). However, reliability of these devices has not been established. We hypothesize that reliability would be affected by both the type of flow sensors and ventilator controllers utilized. Intubated, sedated Sprague Dawley rats (n = 14) were ventilated (control and support modes) utilizing two different ventilators: 1) fixed orifice flow sensor (FOF) and 2) both a hot wire (HWF) and variable orifice flow sensor (VOF), independently. Accuracy of delivered tidal volume was obtained by comparing the displayed volume of the different sensors to breath waveforms acquired using a heated 0–5 L/min calibrated pneumotachograph. Analysis was performed utilizing ANOVA with P ≤ 0.05. Rats mean weight was 472 ± 46 g. For all modes, mean V_TE % difference was demonstrated across all three measuring sensors. For volume control ventilation and pressure control ventilation or time cycled pressure limited assist control, there was a difference between all three sensors. For pressure support ventilation, there was a difference with the HWF only. R-square values were FOF 0.80, HWF 0.54, and VOF 0.16. The accuracy of delivered V_TE is affected by both the flow sensor and ventilator controller to deliver the breath. We speculate that the flow sensor and the controller are associated with varying degrees of flow accuracy and control. We would expect volume accuracy for all modes to be equal if the flow accuracy were related to the inaccuracy of the flow sensors only.

Keywords

Pediatric - critical care - artificial - respiration - monitoring - ventilation